Ortiz guided the 3-year-old daughter of Street Sense to victory for Treadway Racing Stable and trainer Leah Gyarmati, with Sweet Whiskey second and Unbridled Forever third in the field of 13 sophomore fillies. The final time for one-turn mile was a solid 1:34.98 on a fast track.
Gazelle Stakes (gr. II) winner My Miss Sophia, the 4-5 favorite, faded in the stretch after stalking the pace and finished seventh.
Sweet Reason was bred in Kentucky by Brent and Beth Harris and Darley out of the Mt Livermore mare Livermore Leslie.
Riding from near the back of the pack, Ortiz advanced the filly into contention from between horses in upper stretch and then guided her to the outside of 32-1 shot Sweet Whiskey, who had taken the lead from the tiring pacesetter Fiftyshadesofgold.
Sweet Reason, sent off at odds of 9-1, unleashed a terrific turn of foot from the eighth pole to win by half a length over the hard-trying Sweet Whiskey, with John Velazquez aboard.
Sweet Whiskey was four lengths clear of Unbridled Forever and Joel Rosario, with Fiftyshadesofgold three parts of a length farther back in fourth.
Fiftyshadesofgold, pressed by My Miss Sophia and Fashion Plate, who was away a bit slowly from the rail, carved sharp quarter-mile splits of :22.86. and :45.88, before being overtaken by Sweet Whiskey as they completed six furlongs in 1:10.32. As the early leaders gave way, Sweet Reason loomed a big danger and she did not disappoint with a big finish.
"Everything turned out perfectly," Ortiz said after his first Acorn triumph. "She broke, I sat, I waited, waited, waited and turned the corner and saved all the ground I could. Then, I got clear and she took off. Very nice."
Winner of Spinaway Stakes (gr. I) last September at Saratoga Race Course, Sweet Reason was third, nearly eight lengths behind My Miss Sophia in the April 5 Gazelle at Aqueduct Racetrack. She signaled her readiness for a return to top form with a pair of recent bullet moves at Belmont including a half-mile breeze in :45 4/5 May 31.
"After the Gazelle, I didn't like how she was looking," Gyarmati said after her first Acorn win. "I pulled some blood on her. There were little things off, nothing major, probably just wear and tear from the winter. She probably took it harder than I thought she did going into the race. We just did a lot of work on that, lots of vitamins. There wasn't anything major.
"This time we had a fair shot with the pace, I thought," she added. "I thought that if that was my excuse last time, which I was hoping was my excuse, I thought maybe this time I'd get a chance to see, maybe, a different race set up for her."
Sweet Reason, who was second in Belmont's Frizette (gr. I) last fall before finishing a close fourth in the Breeders' Cup Juvenile Fillies (gr. I), won for the fourth time in seven lifetime starts. A $185,000 purchase by Jeff Treadway from the 2012 Keeneland September yearling sale when consigned by Bettersworth Westwind Farms, she has earned $929,000.
Sweet Reason carried 121 pounds and paid $20.80, $9.60, and $6.40 as the third choice in the big field. Sweet Whiskey paid $25 and $13, rounding out an impressive $481 exacta. Unbridled Forever paid $6.40 to show.
Pletcher, trainer of My Miss Sophia, said the favorite "had an off day."
"It wasn't her day," added Javier Castellano, the rider on My Miss Sophia. "She was in a good spot, but she didn't fire."